3-Alkoxy-4-hydroxy-1,2,5-thiadiazoles are described in Journal of Organic Chemistry, page 2823 (1967). However, the thiadiazole derivative of the present invention represented by formula [I] described below and the production process thereof have not been known. Further, the thiadiazole derivative of the present invention represented by formula [III] described below and the agricultural and horticultural fungicide containing the thiadiazole derivative as an active ingredient have not been known.
Further, many compounds having a fungicidal activity are utilized in agriculture but various problems such as the tolerance for plant pathogenic fungi is revealed by continuously using the same or similar chemicals for a long period of time have been indicated and hence the development of novel agricultural and horticultural fungicides which do not reveal such tolerance has been desired.